The present invention relates to ultrasonic visualisation and catheters therefor.
The present invention relates generally to the field of ultrasonic imaging intravascular ultrasound imaging or IVUS in transluminal coronary angioplasty known as PCTA.
In a previously proposed 5 French IVUS device having an annular array of piezo-electronic transducers at its distal end, the array which could comprise sixty-four transducer elements is about 1.6 mm in diameter. In this arrangement the transducer elements were excited in pairs thus necessitating thirty two interconnections and given the size of the catheter outer body, it was possible to route four eight-way ribbon cables within it.
When designing such a catheter with dimensions less than 5 French problems relating to the greatly reduced diameter and thus available space for interconnections are encountered. Excitation signals from an external separate apparatus are routed through a small number of interconnections (for example ten) to individual transducer elements through the use of flip-chip-bonded multiplexers positioned at the distal end of the catheter and proximally to the transducer array. A method of manufacturing the transducer array and associated multiplexers is disclosed in our copending published UK Patent Application No. 2.287,375 in which the assembly is first formed in the flat and then wrapped into a substantially cylindrical configuration. More particularly, the flat assembly comprises the transducer array, the multiplexer chips, electrically conducting multiplexer chips, electrically conducting leads and a suitable matching layer. The use of the multiplexer chips which act as electronic switches permits the use of fewer interconnections which can thus fit into a smaller lumen. In conventional PCTA an incision is made in the femoral region of the patient's leg to introduce a mid-length sheath having a diameter of typically 8 French or 2.66 mm into the femoral artery. A much thinner guide wire (typically 0.014 inches or 0.356 mm diameter) is then introduced via the resulting opening and is manually guided right up to the exact location of the affected region. The affected regions of the coronary arteries follow a tortuous route and the cardiologist relies upon the rigidity of this wire to guide it into place.
Once the end of the guide wire arrives at the required location it is kept firmly in place and in current PCTA/IVUS applications the cardiologist next has to go through an involved procedure of inserting further guide catheters, or sheath catheters prior to finally introducing the IVUS or other treatment catheter.
Keeping the guide wire firmly fixed, a guide catheter of similar dimensions to the mid-length sheath is then inserted over the guide wire, the mid-length sheath still being in place and manually guided through the opening of the aorta stopping a short distance into the coronary artery. There are various versions of guide catheters which usually have the distal ends gently curved or looped depending upon their ultimate destination within the artery system. Contrast opaque dye is then pumped through the guide catheter to flush through the aortic system rendering the cardiac vessels visible on the fluoroscope monitor to enable the cardiologist to visualise the situation.
The device catheter has a central lumen whose diameter is slightly larger (typically 0.017 inches or 0.43 mm) than that of the guide wire. This time, keeping the guide-wire/guide-catheter assembly firmly in place, the device catheter is fed over the guide wire and is simply pushed up the guide wire through the guide catheter.
The progress is monitored by noting the location of an X-ray opaque marker on the moving device catheter relative to the X-ray opaque marker on the fixed guide catheter. When the two markers are coincident the cardiologist knows that the calcified region of interest has been reached. If a balloon catheter is being used saline solution may now be pumped into the balloon to inflate it thereby dilating the affected artery. The results of the procedure are then examined using the imaging device.
The disadvantage of this known system is the inconvenience of having to withdraw one catheter and insert another in order to swap between the PCTA or other treatment procedure and the imaging procedure.